How would you define the term “limiting reactant”?

Hint: Suppose a reaction is the formation of ammonia from hydrogen and nitrogen, and the reaction is:
${{N}_{2}}+3{{H}_{2}}\to 2N{{H}_{3}}$
In this reaction, the hydrogen will be the limiting reactant because if we take 2 moles of hydrogen instead of 3 moles of hydrogen then the reaction will not occur and there will be no enough hydrogen available so that the nitrogen can react.

Complete step by step answer:
When a reaction occurs there is the formation of products and there are many factors that can be used to decide the amount of the formation of the product. So, one of the factors is limiting reagent in the reaction.
There are two parts in the reaction or specifically saying on the reactant side. These are excess reagents and limiting reagents. The one which is more in quantity even after the products are formed in excess reagent and the one which is completely used in the reaction, whose quantity decides the quantity of product formed in the reaction, is called the limiting reagent.
Suppose a reaction is the formation of ammonia from hydrogen and nitrogen, and the reaction is:
${{N}_{2}}+3{{H}_{2}}\to 2N{{H}_{3}}$
Hydrogen is the limiting reagent and nitrogen is the excess reagent.
In the reaction of formation of water:
$2{{H}_{2}}+{{O}_{2}}\to 2{{H}_{2}}O$
Hydrogen is the limiting reactant and oxygen is the limiting reactant.
In the reaction of formation of carbon dioxide:
$2CO+{{O}_{2}}\to 2C{{O}_{2}}$
Oxygen is the limiting reagent and carbon monoxide is the excess reagent.

Note: For finding the limiting and excess reagent in the reaction, the reaction must be balanced. If the reaction is not balanced, the number of moles of the reactants will be wrong which is used for finding the limiting reagent.